Effect of bisphenol A on the early life stage in Japanese medaka (Oryzias latipes)

Japanese medaka (Oryzias latipes) were exposed to bisphenol A (BPA) at the sublethal concentrations of 2.28, 13.0, 71.2, 355, and 1,820 mu g/L (as mea n measured concentrations) in the early life stage from fertilized eggs to 60-d posthatch. Except for the growth and sexual differentiation of the fis h at 60-d posthatch, no effects were observed on hatching success and time to hatching in embryological stage and on mortality and abnormal behavior a nd appearance in hatched larvae. The growth of the fish was suppressed with increasing BPA concentrations, resulting in significant differences in bot h the total length and body weight of medaka at 1,820 mu g/L compared with the controls. When observed for their external secondary sex characteristic s, no males were identified in the 1,820-mu g/L treatment. In addition, his tological examination showed that 32% of fish in the 1,820-mu g/L group had testis-ova composed of both testicular germ cells and oocytes. Consequentl y, the lowest effective concentration for the early life stage of medaka wa s between 355 and 1,820 mu g/L. Since the environmental concentrations of B PA are usually three orders lower than the lowest effective concentration, BPA alone may not affect the early life stage of wild fish populations.